Cytokines are small proteins that play an important role in intercellular communication. Cytokines can be classified based on their structure, the largest group being the four-α-helix bundle family. This family can, based on the use of receptors, further be divided into the interferon (IFN) and interleukin (IL)-2, -3, -10 and -12 subfamilies. The α-helical bundle cytokines are important as possible biopharmaceuticals for treatment of human diseases. As non-limiting examples, erythropoietin is used for treatment of anemia or red blood cell deficiency, somatotropin for treatment of growth hormone deficiency, and interleukin-2 in the treatment of cancer.
Within the α-helical bundle cytokines, type I IFNs belong to a cytokine family having important biological functions. In humans, there are 17 different type I IFNs (13α, β, ε, κ, ω), which signal through a ubiquitously expressed cell surface receptor composed of two chains IFNAR1 and IFNAR2. The assembling of the IFN-receptor complex initiates the activation of several signal transduction pathways that, depending upon the cell type, modify cellular differentiation and/or functions.
By acting on virtually every cell type, type I IFN is able to prevent productive viral infection. In addition, it exhibits marked antiangiogenic and proapoptotic effects. Type I IFNs are also deeply implicated in the regulation of several functions of the innate and adaptive immunity, as well as on bone homeostasis. It acts particularly on the activation/differentiation of dendritic cells and osteoclasts. The type I IFN system is, in fact, critically important for the health of mammals.
Preclinical studies in mice have established a remarkable efficacy of type I IFN for the treatment of both viral or tumor diseases. Noteworthy, mice cured of an experimental tumor by IFN treatment have been found immunized against the initial tumor, suggesting that IFN acts not only to engage the processes of tumor rejection but also to break the immune tolerance against the tumor. Based on these studies, IFNα was approved in clinics for the treatment of both viral infection and cancer. More recently, IFNβ was shown to be effective in relapsing-remitting multiple sclerosis and was also approved for this pathology. Unfortunately, the clinical efficacy of IFN was often found disappointing and today, other therapeutic strategies such as specific antiviral compounds, chemotherapies and monoclonal antibodies have, when possible, largely supplanted IFN broad application. Today, IFN is the first line therapeutic choice for only HBV and HCV chronic infections and for a limited number of tumors.
The efficacy of type I IFN in clinical practice is limited by ineffective dosing due to significant systemic toxicity and side effects, including flu-like syndrome, depression, hepatotoxicity, autoimmune disease, thyroid dysfunction and weight loss. It would thus be highly worthwhile to target IFN activity toward only the cellular population that should be treated with IFN (e.g., infected organ or tumor mass) or activated by IFN (e.g., subsets of immune cells).
In order to solve or limit the systemic toxicity of cytokines, specific targeting of cytokines by antibody-cytokine fusion proteins has been proposed (Ortiz-Sanchez et al., 2008). Rossi et al. (2009) specifically disclose CD20-targeted tetrameric IFNα, and its use in B-cell lymphoma therapy. However, the fusion maintains its biological activity, and is even more active than commercial pegylated IFN, which means that the unwanted side effects in human treatment would still be present, or would even be more severe. WO2009039409 discloses targeted IFN and its apoptotic and anti-tumor activities. Not only does the patent application disclose the fusion of an antibody as targeting moiety with wild-type IFN, but also with mutated IFN. However, it is stated that the IFN fragment should retain its endogenous activity at a level of at least 80%, or even at a higher level than wild-type IFN. Also, in this case, the fusion is retaining the unwanted side effects of the wild-type.